1. Field of the Invention
The present invention relates to a semiconductor device having a circuit including a thin film transistor (hereinafter, referred to as a TFT) in which a channel formation region is formed using an oxide semiconductor film, and a method for manufacturing the same. For example, the present invention relates to an electronic appliance in which an electro-optical device typified by a liquid crystal display panel or a light-emitting display device including an organic light-emitting element is mounted as its component.
Note that the semiconductor device in this specification indicates all the devices that can operate by using semiconductor characteristics, and an electro-optical device, a semiconductor circuit, and an electronic appliance are all included in the semiconductor devices.
2. Description of the Related Art
In recent years, active matrix display devices (such as liquid crystal display devices, light-emitting display devices, or electrophoretic display devices) in which a switching element of a TFT is provided in each of display pixels arranged in a matrix have been actively developed. An active matrix display device includes a switching element in each pixel (or each dot), which is advantageous in that it can be driven at lower voltage than a passive matrix display device in the case where the pixel density increases.
In addition, the technology, in which a thin film transistor (TFT) or the like is manufactured using an oxide semiconductor film in a channel formation region and such a TFT is applied to electronic devices or optical devices, has attracted attention. For example, there is a TFT using zinc oxide (ZnO) for an oxide semiconductor film or a TFT using InGaO3 (ZnO)m for an oxide semiconductor film. The technology, in which a TFT using such an oxide semiconductor film is formed over a light-transmitting substrate and used as a switching element or the like of an image display device, is disclosed in Reference 1 and Reference 2.